String.IndexOf() and String.SubString() ?
ex. To separate "myemail@myprovider.com" into 'email_name' and 'provide_namer' (hint: separated by the @ character)
You'd find the Index of the "@" character, using .IndexOf(), and copy the string, using .SubString() - from its first character up until the @ character. To get the 'provider' part of the string you'd .SubString() starting at the @ character's index + 1 and go to the last character (in this example).